1. Field of the Invention
The present invention relates to solid electrolyte bodies having oxygen ion conductivity and gas sensors having a gas sensor element equipped with the solid electrolyte body.
2. Description of the Related Art
A gas sensor detects a concentration of a specific gas such as oxygen gas contained in a mixture gas such as exhaust gas emitted from internal combustion engines. Such a gas sensor uses a solid electrolyte body having oxygen ion conductivity. In more detail, a gas sensor is equipped with a gas sensor element, a heater section, etc. The gas sensor element has a solid electrolyte body and a pair of electrodes. For example, the electrodes are formed on both surfaces of the solid electrolyte body, respectively. When receiving electric power, the heater section generates heat energy. The generated heat energy heats the gas sensor element, and a temperature of the gas sensor element rises. A patent document, Japanese patent laid open publication No. S53-139595 has disclosed such a gas sensor having such a conventional structure. In particular, it is requested for the solid electrolyte body in the gas sensor element to have and maintain specific functions, such as a highly operational reliability and a quick responsiveness to a change of a concentration of a target gas to be detected, without causing cracks under harsh environment.
Also, a zirconia sintered body has been developed as a solid electrolyte body to be used in gas sensor element. The zirconia sintered body contains oxygen ion conductive material and a zirconia sintered body. In the solid electrolyte body, the oxygen ion conductive material and zirconia sintered body are mixed under a predetermined compound ratio. The oxygen ion conductive material is made of zirconium oxide and yttrium oxide which have been mixed in a predetermined compound ratio. The zirconia sintered body is made of aluminum oxide and silicon oxide which have been mixed in a predetermined compound ratio.
Recently, there is a strong demand to save a fuel consumption of internal combustion engines mounted on vehicles, etc. and an increasing requirement to provide a gas sensor with highly quick responsiveness under low temperature environment. However, there is a possible problem of causing cracks in a gas sensor equipped with the conventional solid electrolyte body, and having a low responsiveness when the gas sensor is used at a low temperature of approximately not more than 350° C. That is, low temperature deterioration occurs in the conventional solid electrolyte body.